THE OLFACTORY-GUSTATORY BASIS OF FOOD PREFERENCE IN THE HERBIVOROUS PROSOBRANCH, LITTORINA LITTOREA (LINNAEUS)

Studies of food preference often measure the rate of consumptionof prey items by a predator; this confounds the factors determiningattractiveness and edibility, ignoring the fact that preferencesare probably resolved at the pre-ingestive stage of a consumer'sfeeding behaviour. In this paper, a novel technique has beendeveloped to measure the importance of chemical stimuli to feed,perceived by olfactory and gustatory means, as determinantsof the subsequent feeding behaviour of the generalist intertidalherbivore,Littorina littorea (L.). Cell-free extracts of a rangeof algae were presented simultaneously, impregnated in artificialcellulose-based substrates. Subsequent ranking of feeding preferencesreveals hierarchies which correspond with those establishedby other workers, using intact algae to feed L. littorea. Extractsof ephemeral early successional species (e.g. Ulva lactuca,Porphyra umbilicalis) generally provoke a more positive feedingresponse than perennial late successional species (e.g. Fucusvesiculosus, Asco-phyllum nodosum). Animals fed a preferredalga (Ulva lactuca) prior to preference trials displayed a reductionin the strength of preference relative to starved animals. Therewas no evidence of ‘switching’ of preference rankingsdue to satiation, however. These findings confirm the importanceof olfactory-and gustatory-mediated feeding behaviour as theprimary determinant of food preference in L. littorea. Theyare consistent with the hypothesis that the factors which determinethe attractiveness of a food type, such as chemical cues, arethe criteria by which consumers predict the value of that food.